cmd/internal/obj/riscv: correct CALL reloc symbol handling

Move the CALL reloc symbol back to p.From.Sym, rather than p.To.Sym - while
p.To.Sym is the correct final location, the call to lowerJALR flips the p.To
and p.From addresses (and proves that this form of obj.Prog rewriting is not
a good idea).

Updates #27532

Change-Id: Iaf9fa24b05bda32b963f8d243401c6cd82c1355c
Reviewed-on: https://go-review.googlesource.com/c/go/+/212759Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/riscv/obj.go

@@ -58,14 +58,14 @@ func jalrToSym(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc, lr int16) *ob
 	p.Mark |= NEED_PCREL_ITYPE_RELOC
 	p = obj.Appendp(p, newprog)
 
-	// Leave p.To.Sym only for the CALL reloc in assemble.
+	// Leave Sym only for the CALL reloc in assemble.
 	p.As = AJALR
 	p.From.Type = obj.TYPE_REG
 	p.From.Reg = lr
+	p.From.Sym = to.Sym
 	p.Reg = 0
 	p.To.Type = obj.TYPE_REG
 	p.To.Reg = REG_TMP
-	p.To.Sym = to.Sym
 	lowerJALR(p)
 
 	return p